Cutting bit, cutting tool and method for machining, especially rotationally symmetrical work piece surfaces

ABSTRACT

A cutting bit has the basic form of a prism, including two substantially parallel top and bottom surfaces and at least three lateral surfaces running substantially perpendicular to the top and bottom surfaces. A cutting edge is embodied in the transition area from at least one of the lateral surfaces to the top or bottom surface and wherein the at least one lateral surface has alternate projecting and recoiling sections viewed from above or from below. Effective main cutting edges are embodied at least in the area of the projecting sections, and wherein optionally secondary cutting edges extend from the relatively projecting main cutting edges backwards along the recoiling sections for at least at a given cutting depth.

BACKGROUND OF THE INVENTION

The present invention relates to a cutting bit, a cutting tool and amethod for machining.

Similar cutting bits, cutting tools and a machining method for usetherewith are described in German Patent Application No. 41 35 681 andthe corresponding European Patent Application No. 542 026.

That publication describes an apparatus and a method for machiningrotationally symmetrical work piece surfaces, wherein various cuttingbits are arranged along a disc-shaped tool carrier and are engagedsuccessively with the work piece for machining. Therein, final machiningis in the form of a roughing-down and smoothing operation during which acutting bit with a substantially zigzag main cutting edge, i.e. formedby projecting and recoiling sections of the cutting bit, is advancedfirstly in a radial direction, and then in a roughing-down operation acertain layer thickness is taken off the work piece surface formachining, whereupon the tool is then moved axially in order to performa smoothing operation by means of which fine machining is effected.

U.S. Pat. No. 4,867,616 discloses a cutting bit which has the basic formof a prism, comprising two substantially parallel top and bottomsurfaces and four lateral surfaces substantially perpendicular to thetop and bottom surfaces, wherein cutting edges are formed at thetransition of the lateral surfaces to the top and bottom surfaces, andwherein those lateral surfaces are not even, and, in the plan view ontothe top surface or bottom surface, has alternate projecting andrecoiling sections, wherein effective sections of main cutting edges areformed in the region of the projecting sections, and wherein secondarycutting edges extend from the relatively projecting sections of the maincutting edges rearwardly along the recoiling sections at least by apredetermined insertion depth.

With that cutting bit, the secondary cutting edges are bent relative tothe main cutting edges partially by 60° and in the corner regions by 45°Furthermore, the machining surfaces are formed by recesses which areassociated individually with each section of main cutting edge, whereinin the central region of a main cutting edge an angle of between 62° and72° results between the machining surface and the main free surface.

Corresponding cutting bits are mounted on a milling cutter in such a waythat their main cutting edges slightly overlap, and the main cuttingedges of a cutting bit alternatingly cover over the recoiling regions ofa successive cutting bit, so that the secondary cutting edges onlyengage with the tool by way of their regions which are directly adjacentto the main cuts. A corresponding tool is provided exclusively for feedin a radial direction, for the purpose of milling grooves, or the like,in a tool, for example.

OBJECTS AND SUMMARY OF THE INVENTION

In the face of this prior art, the aim of the present invention is tocreate a cutting bit, a cutting tool, and a corresponding method formachining work pieces, wherein the cutting bit is intended to be fed notonly radially but also axially during machining the work pieces, andwherein the corresponding work piece surfaces should be of good qualityand efficiently produced, i.e. within strict tolerances.

The selection of special angles firstly permits a positive cuttinggeometry both during radial and axial feed to the work piece, and,additionally, the reaction forces occurring are kept relatively low, sothat neatly defined work piece surfaces can be produced within stricttolerances.

The design of the cutting bit according to the invention enables thecutting bit to be inclined somewhat downwardly relative to the feeddirection, wherein a free surface is prepared for improved radial feedof the cutting bit to the work tool or to the work piece surface formachining, on the one hand, whilst it is still possible to maintain apositive cutting edge geometry whereby the cutting forces occurring arereduced.

With respect to a corresponding tool, the problem forming the basis ofthe invention is solved in that in the tool a corresponding cutting bitis used, and in that the tool seat has a supporting surface for the topor bottom surface of the cutting bit, which is inclined such that itfalls away at an angle of between 8° and 12° relative to the radial feeddirection.

The corresponding method uses a cutting bit and a cutting tool of theafore-mentioned kind, wherein the radial feed of the cutting bit towardsthe work piece surface is such that the top and bottom surfaces areinclined such that they fall away to the front relative to that feeddirection.

The terms, “radial feed direction” and “axial direction” refer herein,first and foremostly, to a work piece which is rotating about an axis,so that during machining a rotationally symmetrical surface is producedon that work piece. Therein, the feed generally takes place in such away that the cutting edge and the axis of rotation of the rotating workpiece lie in a common plane, and feed of the cutting bit also takesplace exactly in that plane, initially in a radial direction. After thedesired diameter of the rotationally symmetrical work piece hasessentially been obtained, the cutting bit moves axially relative to thework piece for fine machining to ensue, and, in particular, the regionswhich initially were still remaining between the interrupted maincutting edges are removed by axial rotation.

However, the invention can be extended thoroughly to machining methodsin which non-rotationally symmetrical surfaces, e.g. even surfaces, aremachined, and the cutting bit is accordingly arranged on a rotatingtool. In such a case, the terms, “radial feed” and “axial feed” aredefined in relation to the axis of rotation of the tool.

According to the invention, the complementary angle cc between themachining surface and a plane which is perpendicular to the plane of thefree surfaces of the main cutting edges is between 14 and 18°, and, witha preferred embodiment, it is 16°.

This means, for example, that in the case of the preferred embodimentmentioned latterly, the seating for the cutting bit, or the top andbottom surfaces of the cutting bit can be inclined at an angle ofapproximately 10° relative to the feed direction, wherein a positivemachining angle of approximately 6° nonetheless remains in the region ofthe main cutting edge. The inclination of the top and bottom surfaces byapproximately 10° relative to the feed direction means at the same timethat the plane of the free surfaces, which, due to the prismatic basicform of the cutting bit, extends substantially perpendicularly to thetop and bottom surfaces, is likewise inclined by 10° relative to atangent on the work piece surface in the region of the active maincutting edge, so that an effective free angle of about 10° is formed. Itwill be appreciated that in the case of a rotating work piece surfacebecause of the curvature of the surface generated the free angle becomesincreasingly larger directly behind the cutting edge.

This cutting geometry and arrangement of the cutting bit produce verysmall cutting forces so that harmful vibration of the work piece, suchas can occur with different cutting edge geometries, is largely avoided.At the same time, wear to the cutting edge is reduced.

In addition, the geometry of the cutting bit which is actually selectedenables main cutting edges 10 to be formed both at the transition of therespective lateral surface to the top surface as well as at thetransition of that lateral surface to the bottom surface of the cuttingbit. Therefore, after one of the main cutting edges of the cutting bithas become worn, the cutting bit can be turned and used again. Thiseffect is rendered two-fold in a preferred embodiment of the inventionwherein the cutting bit has the basic form of a cuboid with two shorterlateral surfaces and two longer lateral surfaces, wherein cutting edgesare formed on each of two oppositely disposed lateral surfaces, and, tobe more exact, at the transition to the top and bottom surfacerespectively, so that a total of four main cutting edges is formed whichare interrupted main cutting edges corresponding to the projecting andrecessed regions of the lateral surfaces and to which respectivesecondary cutting edges are adjacently disposed which extend at least alittle way into the recessed regions of the lateral surfaces inquestion.

In this embodiment, there is a total of four cutting edges, each ofwhich can be changed over after the cutting edges have become worn. Thismakes the cutting bit according to the invention very economical to use.

One embodiment of the invention is particularly preferred wherein theindividual sections of the interrupted main cutting edge are maincutting edge sections lying on a common straight line. This facilitatesthe production of rotationally symmetrical surfaces.

In the preferred embodiment, the secondary cutting edges which areadjacent to the main cutting edge sections, should, in the plan viewonto the top or bottom surface, be bent at an angle of between 65° and70°, in particular of 67.5°, relative to the main cutting edges.Therein, each of the main cutting edge sections should be delimited assymmetrically as possible on both sides of a corresponding secondarycutting edge. In this way, an axial smoothing movement in bothdirections is possible, which simplifies the corresponding machiningmethods.

Preferably, at least two projecting regions, and thus two main cuttingedge sections, are provided 5 along the lateral surfaces concerned,these main cutting edge sections being interrupted by a recessed region,wherein secondary cutting edges extend from the ends of the main cuttingedges into this recessed region. However, one embodiment of theinvention is particularly preferred wherein a total of three projectingregions is provided, wherein one is provided centrally in the middle ofthe corresponding lateral surface and defines a centrally arranged maincutting edge, whilst the other two projecting regions are arranged inthe vicinity of the oppositely disposed ends of that lateral surface,and form main cutting edge sections there which are delimited at thetransition to the respective other lateral surfaces by relatively shortsecondary cutting edge sections, wherein the length of those secondarycutting edge sections is less than the depth of the recessed regions ofthe lateral surfaces.

One embodiment of the invention is particularly preferred whereinadditional recesses in the machining surfaces are formed within theprojecting regions, which recesses impart to the secondary cutting edgesa positive cutting edge geometry during axial feed.

Furthermore, the angle formed between the secondary cutting edges andthe main cutting edges, in conjunction with the free surfaces of thesecondary cutting edges which are angled in the same way relative to thefree surfaces of the main cutting edges, and in conjunction with theinclination of the cutting bit in the feed direction, during the axialfeed causes the free surfaces of the secondary cutting edges to form apositive free angle with the work piece surfaces produced by thesecondary cutting edges. This feature also reduces the axial cuttingforces and feed forces which additionally helps towards smoothermovement of the rotating work piece, or, in the case of a rotating tool,towards smoother movement of the tool, with the result that veryhigh-quality surfaces can be produced by this kind of machining underconditions which are also very economical.

Expediently, a corresponding cutting bit has a central bore, the axis ofwhich extends perpendicularly to the top and bottom surface. This borecan be tapered somewhat in the center of the cutting bit between the topand bottom surface, or, in the region of the top and bottom surface, itcan define a seating of variable conicity for a tightening screw, sothat the cutting bit can be fastened to an appropriate seating of anappropriate tool by the use of an appropriate tightening screw.

The geometry defined herein above of the cutting bit according to theinvention also makes it possible advantageously and economically for thecutting bit to be able to be formed under compressive conditions whichsignificantly reduces the production cost of such a cutting bit. At thesame time, the cutting bit has a positive cutting geometry and apositive free angle, but nonetheless has cutting edges both at the topsurface as well as at the bottom surface respectively, so that thecutting bit according to the invention combines excellent cuttingproperties with a very cost-effective method of manufacture, and,additionally, economical wear behavior.

The corresponding cutting tool is adapted to the cutting bit accordingto the invention, so that the seating for the cutting bit in that toolslopes relative to the feed direction of the tool at an angle of between8 and 12°. In addition, the seating has a threaded bore for receiving atensioning screw for fastening a corresponding cutting bit.

With the method according to the invention, preferred embodiments arecharacterized in that the angle of inclination of the top and bottomsurfaces relative to the feed direction is within the range of 8 and12°, wherein an angle of 10° has proven to be expedient in practice.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and possible applications of the presentinvention will emerge from the following description of a preferredembodiment and the accompanying drawings, wherein:

FIG. 1 shows a view in perspective of a cutting bit according to theinvention,

FIG. 2 shows a view in plan (on a smaller scale than FIG. 1) from aboveonto the top surface 2 of the cutting bit according to FIG. 1,

FIG. 3 shows, schematically, a side view of a cutting bit in theprovided working position,

FIG. 4 is a view, partly in section, looking along the cutting planeIV—IV of FIG. 3,

FIG. 5 shows, on a very large scale, and in a plan view from above, oneof the projecting regions of a lateral surface,

FIG. 6 is a side view, on a large scale, of the cutting edge region, andFIG. 7 is a view, partly in section, of a cutting plane along the lineVII—VII of FIG. 6.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

The view in perspective of FIG. 1 shows the cutting bit 1 which isessentially cuboid or prismatic in its basic shape and which has twosubstantially even and parallel top and bottom main surfaces 2 and 3 andlateral surfaces which extend perpendicularly thereto and which aredenoted by the reference numerals 4, 5, 6 and 7 in FIG. 2. Therein, theoppositely disposed lateral surfaces 4 and 6 are also substantiallyeven, whereas the remaining shorter oppositely disposed lateral surfaces5 and 7 define alternate projecting regions 11 and recessed regions 12.Therein, however, the front surfaces 13 (see FIG. 1) of all projectingregions 11 are, in turn, disposed in a common plane, and the recessedregions 12 are of substantially the same depth and therefore, are offsetto the same extent, back from the plane defined by the surfaces 13. Thecutting line between the top and bottom surfaces 2 and 3 together withthe oppositely disposed structured lateral surfaces 5 and 7 defines maincutting edges 8 which each extend accordingly along the farthestrecessed regions of the top edge of the front surfaces 13, and secondarycutting edges 9 which extend along a section of the rearwardly extendingsections of the surfaces 5 and 7. In the transitional region to thelateral surfaces 5 and 7, the top and bottom surfaces 2, 3 each havechannels or recesses by which machining surfaces 10 are formed, on theone hand, which are adjacent to the cutting edges 8 and 9, whereinmachine shaping surfaces 16 are disposed adjacently to the inside of thecutting bit and extend beyond the recessed regions 12 into the main partof the cutting bit 1, finally terminating at the plane of the top andbottom surfaces 2 and 3.

The cutting bit has the symmetry of a cuboid, i.e. it is laterallyreversed with respect to three mutually perpendicular planes whichextend parallel to the peripheries of the cuboid through the center ofsame, or, in other words, which extend rotationally symmetricallyrelative to rotations through 180° about three respective axes,perpendicular to each other, and passing through the center of thecuboid. In concrete terms, this means that each of the cutting bits 1have four different cutting edge regions which can be used one after theother, and which, out of a group consisting of three main cutting edges8, have secondary cutting edges 9 which are respectively adjacent to amain cutting edge 8.

FIG. 3 is a schematic side view of the cutting bit 1 in an activecutting position during radial feed. The radial feed direction isindicated by an arrow RF, wherein the active cutting edge 8 is disposedexactly at the height of the axis of a rotating work piece, not shownhere. On contact with the work piece, the vertical line 17 defines theposition of a plane tangential to the machining surface of the rotatingwork piece.

As can be seen, the top and bottom surfaces 2 are inclined relative tothe feed direction by an angle of about 10°, and therefore the surface13 which defines a free surface relative to the cutting edge 9 isinclined by an angle of 10° to the tangential plane 17 on the surface ofthe work piece. However, at the same time, the machining surface 10which is adjacent to the cutting edge 8 is inclined inwardly by at anangle α of about 16° relative to the top surface 2 of the cutting bit(and also relative to a plane P which is perpendicular to the plane ofthe front surfaces 13 of the projection regions 13), so that the cuttingedge 8 still has a positive cutting geometry with a positive machiningangle of about 6° relative to the surface of the work piece defined bythe plane 17. A positive machining angle generally reduces the cuttingforces occurring during machining. Another line which is parallel to theplane 17 indicates the maximum cutting depth provided for the cuttingbit according to the invention. An end 16 of the machining surface 10disposed remotely from the main cutting edge is recessed relative to acenter portion 2 a of the top surface 2 (see FIG. 6).

If the cutting bit penetrates into the surface of the work piece to theprovided cutting depth, grooves of trapezoidal cross-section areproduced in the surface of the work piece by the three cutting edges 8and the adjacent secondary cutting edges 9. The cutting bit 1 is thenmoved relative to the work piece axially, i.e. perpendicularly to thepaper plane in FIG. 3, or, as shown in the frontal view of FIG. 4, inthe paper plane, and, to be more exact, alternatively in both axialdirections AF, AF′. As a result of this axial forward movement thesecondary cutting edges 9 remove the material of the work piece whichcontinues to exist in the grooves already produced. Due to the specialshape and arrangement of the projections 11 and of the recessed regions12 in conjunction with the inclination of the surfaces 2 and 3 relativeto the horizontal, a positive free angle is also obtained for thesecondary cutting edges 9 during axial feed. This is already indicatedin FIG. 4 and is also illustrated more clearly in the larger scaledrawings of FIGS. 5 to 7.

FIG. 5 is a view, from above, onto the machining surface 10 of one ofthe projecting regions 11 which is shown here merely in broken awaymanner. Therein, the main cutting edge 8 and the two adjacent secondarycutting edges 9 which define the machining surface 10 can be seen. Abroken line is used to indicate a section plane VII—VII, wherein thecorresponding sectional view is reproduced in FIG. 7. FIG. 6 is a sideview of the cutting edge region of a corresponding cutting bit. Heretoo, the cutting bit is shown in its inclined working position, whereinthe angle of inclination of the top surface 2 relative to the horizontalfeed direction, or rather, the angle of inclination of the front freesurface 13 relative to the surface of the work piece is less than theangle of inclination of the machining surface 10 relative to the surface2, so that the cutting edge 8, as already mentioned, retains itspositive cutting geometry. The surfaces 15 which likewise extendperpendicularly to the top surface 2 and which define secondary freesurfaces relative to the secondary cutting edges 9 define the length ofthe secondary cutting edges 9. FIG. 6 also shows the cutting planeVII—VII, and the plan view of that cutting plane is shown in FIG. 7. Thecutting plane VII—VII extends in the region of the secondary cuttingedge 9, and by looking at FIGS. 5 and 6 in conjunction with each otherit can be seen that from a region set further back at the top on thesecondary cutting edge 9 the cutting plane VII—VII moves down towardsthe front free surface 13, and finally intersects it.

Since the secondary cutting edges 9 are angled somewhat relative to themain cutting edges 8 by an angle β of between 65 and 75°, preferably67.5° and the secondary free surfaces 15 are angled accordingly by thesame angle relative to the main free surfaces 13, a trapezoidal shaperesults in the plan view of the cutting plane, shown by shading in FIG,7, so that in that cutting plane which is shown in FIG. 7 and which isalso the plane of the axial feed direction of the cutting bits, the topmachining surface 10 and the secondary free surface 15 form an angle ofless than 90°. Therefore, for the secondary cutting edges too, apositive free angle results which is actually about 4° in the embodimentshown. Moreover, the machining surfaces 10 could also have recesses inthe projecting regions 11, so that the secondary cutting edges 9 couldfurthermore also have a positive cutting geometry, but this does notexist in the embodiment shown in the drawings.

Due to the fact that all surfaces delimiting the projecting regions 11and the recessed regions 12 extend exactly perpendicularly to the topand bottom surfaces 2 and 3, wherein the lateral surfaces 4 and 6obviously also extend perpendicularly to those top and bottom lateralsurfaces 2 and 3 (as also expressed by the term, “basic form of aprism”), the cutting bit according to the invention can be formed undercompressive conditions, which makes production relativelycost-effective. Nonetheless, the cutting bit has a total of four cuttingedge regions which can be changed over and used one after the other, andeach of the cutting edge regions has a positive cutting geometry atleast at the main cutting edges, and a positive free angle is formedboth at the main free surfaces as well as at the secondary freesurfaces. This special geometry assists in minimizing the cutting forceswhich occur, which results in the cutting bit being particularlysuitable for fine machining and/or smoothing operations because the workpiece is then also less easily inclined to shake or vibrate, therebyproducing very smooth and neater surfaces. At the same time, due to thedivided up cutting edges, the cutting insert is also suitable for roughmachining, or roughing-down work, i.e. whilst the work pieces arerotating, the cutting bit can be used initially to form groovesradially, wherein the regions which have remained in the region of theinsertion depth are then removed by axial forward and backwardmovements, whereupon the insertion operation can be repeated, and,finally, the last insertion operation, possibly employing a smallerinsertion depth, is concluded by way of the final smoothing operationwhich takes place by axial forward and backward movements.

Therefore, the cutting bit according to the invention combinescost-effective manufacture with favorable wear behavior, greaterversatility, greater economical efficiency due to the multiple,exchangeable cutting edges, and, finally, a very high machining quality.As already mentioned, the cutting bit could also be used to machine evensurfaces, if it is secured to a rotating tool, for example, at thenegative angle of attack relative to a surface 17 of the work piece, asdefined in FIG. 3.

What is claimed is:
 1. A cutting bit having the general form of a prism,comprising two substantially parallel top and bottom main surfaces andat least three lateral surfaces extending substantially perpendicularlyto the main surfaces, wherein a cutting edge is formed at a transitionbetween at least one of the lateral surfaces and at least one of themain surfaces; the at least one lateral surface including alternatingprojecting sections and recessed sections as the cutting bit is viewedin plan; each projecting section including a machining surface visiblein plan view, and a front surface intersecting the machining surface toform a main cutting edge; each projecting section including at least onesecondary edge joined to a respective main cutting edge and extendingalong one of the recessed sections; the machining surfaces being definedby the at least one main surface; the front surfaces being defined bythe at least one lateral surface; each machining surface being inclinedrelative to its associated main cutting edge in a direction toward theopposite main surface to form a first angle in the range of 14° to 18°with an imaginary plane disposed perpendicular to the respective frontsurface; each secondary edge being inclined from its respective maincutting edge by a second angle in the range of 65° to 70° as viewed inplan.
 2. The cutting bit according to claim 1 wherein the second angleis 67.5°.
 3. The cutting bit according to claim 1 wherein the secondaryedges are disposed symmetrically relative to the respective main cuttingedges.
 4. The cutting bit according to claim 1 wherein there are twopairs of lateral surfaces; one of the pairs being shorter than the otherpair as the insert is viewed in plan; the shorter pair intersecting theat least one main surface to form the cutting edges.
 5. The cutting bitaccording to claim 4 wherein the shorter pair intersect both of the mainsurfaces to form the cutting edges at both a top and bottom of theinsert.
 6. The cutting insert according to claim 1 wherein the secondaryedges constitute cutting edges.
 7. The cutting insert according to claim1 further including a through-hole extending through both of the mainsurfaces.
 8. The cutting insert according to claim 1 wherein additionalrecesses are formed in the machining surfaces which impart to thesecondary cutting edges a positive cutting geometry during axial feed ofthe cutting bit.
 9. The cutting bit according to claim 1 wherein the atleast one main surface includes a center portion; the machining surfacesbeing inclined such that ends of the machining surfaces situatedremotely of the main cutting edges are recessed with respect to thecenter portion.
 10. A cutting tool including a cutting bit, the cuttingbit having the general form of a prism, comprising two substantiallyparallel top and bottom main surfaces and at least three lateralsurfaces extending substantially perpendicularly to the main surfaces,wherein a cutting edge is formed at a transition between at least one ofthe lateral surfaces and at least one of the main surfaces; the at leastone lateral surface including alternating projecting sections andrecessed sections as the cutting bit is viewed in plan; each projectingsection including a machining surface visible in plan view, and a frontsurface intersecting the machining surface to form a main cutting edge;each projecting section including at least one secondary edge joined toa respective main cutting edge and extending along one of the recessedsections; the machining surfaces being defined by the at least one mainsurface; the front surfaces being defined by the at least one lateralsurface; each machining surface being inclined relative to itsassociated main cutting edge in a direction toward the opposite mainsurface to from a first angle in the range of 14° to 18° with animaginary plane disposed perpendicular to the respective front surface;each secondary edge being inclined form its respective main cutting edgeby a second angle in the range of 65° to 70° as viewed in plan.
 11. Amethod for machining work piece surfaces, comprising the steps of: A)feeding radially toward the workpiece a cutting bit having the generalform of a prism, comprising two substantially parallel top and bottommain surfaces and at least three lateral surfaces extendingsubstantially perpendicularly to the main surfaces, wherein a cuttingedge is formed at a transition between at least one of the lateralsurfaces and at least one of the main surfaces; the at least one lateralsurface including alternating projecting sections and recessed sectionsas the cutting bit is viewed in plan; each projecting section includinga machining surface visible in plan view, and a front surfaceintersecting the machining surface to form a main cutting edge; eachprojecting section including at least one secondary edge joined to arespective main cutting edge and extending along one of the recessedsections; the machining surfaces being defined by the at least one mainsurface; the front surfaces being defined by the at least one lateralsurface; each machining surface being inclined relative to itsassociated main cutting edge in a direction toward the opposite mainsurface to form a first angle in the range of 14° to 18° with animaginary plane disposed perpendicular to the respective front surface;each secondary edge being inclined from its respective main cutting edgeby a second angle in the range of 65° to 70° as viewed in plan; whereinthe cutting bit being inclined relative to the direction of feed andforms a positive angle of more than 8° with a tangential plane lying onthe respective main cutting edge, and B) moving the cutting bit axiallyrelative to the workpiece for fine machining.